Microelectromechanical systems (MEMS) sensors are widely used in applications such as automotive electronics, inertial guidance systems, household appliances, consumer electronics, protection systems, and many other industrial, scientific, engineering, and portable systems. Such MEMS sensors are used to sense a physical condition such as, for example, acceleration, pressure, angular rotation, or temperature, and to provide an electrical signal representative of the sensed physical condition to the applications and/or systems employing the MEMS sensors. The applications and/or systems may utilize the information provided by the MEMS sensor to perform calculations, make decisions, and/or take certain actions based on the sensed physical condition.
The electromechanical characteristics of each MEMS sensor can differ due to a variety of factors (e.g., manufacturing tolerances, slight differences in processing depending upon where and when the MEMS sensor was manufactured, and so forth). This means that the electrical output of a MEMS sensor responsive to a certain magnitude of stimulus might differ from the electrical output of a second MEMS sensor responsive to a stimulus of the same magnitude. Because systems employing MEMS sensors may use the electrical output to calculate the extent of the stimulus, and may use the result of that calculation to determine whether to take a certain action, it is important that the electromechanical characteristics of the MEMS sensors be identified and evaluated such that a system employing MEMS sensors can be compensated (for offset) and calibrated (for gain) in order to correlate a given electrical output from the MEMS sensor to a specific amount of applied stimulus.
Typically, the identification and evaluation of electromechanical characteristics of a MEMS sensor system is accomplished by applying an actual mechanical stimulus (for example, an acceleration force) to the MEMS sensor system, measuring the electrical response, and storing values representative of the MEMS electromechanical characteristics in the system, along with trim values representative of any “correction” or calibration factors that need to be applied to the electrical output of the MEMS sensor in light of the MEMS electromechanical characteristics. Application of trim value to the MEMS output can help to ensure that the MEMS sensor output corresponds to the magnitude of the applied stimulus.
Although physically applying various mechanical stimuli to systems employing MEMS sensors can serve to provide calibration data, i.e., trim values, so that the system can function properly, such mechanical testing can be expensive, time-consuming, and potentially damaging to the system being tested. Furthermore, the need to mechanically test a variety of systems and applications employing MEMS sensors can require numerous test stations to be designed and built for each application to be tested, further increasing the cost and time associated with such testing. In addition, although mechanical testing prior to shipment of systems employing MEMS sensors can provide trim values, such testing ignores the fact that over time (and as a result of use or damage), the electromechanical characteristics of the MEMS sensor can change, making the initial calibration trim values no longer appropriate.